JPH0372019A - Hearth roll for steel heat treatment furnace - Google Patents

Abstract

PURPOSE:To reduce the cost and labor of roll maintenance by forming a surface layer laminated concentrically and alternately with ceramic films and metallic films in multiple layers on the barrel part of the roll. CONSTITUTION:The roll barrel part 20 of the hearth roll for the heat treating furnace for steel material is constituted of a base material 21 of the barrel part and the surface layer 22 of the barrel part formed on the front surface thereof. The surface layer 22 is formed by alternately and concentrically laminating the ceramic films a and the metallic films b in multiple layers. The film thickness of the metallic film b is specified to 10 to 100mum and the film thickness of the ceramic film a is specified to 5 to 100mum, The surface quality of the steel material to be heated is improved and stabilized in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a hearth roll that is a means for conveying steel material in a steel heat treatment furnace.

[Conventional technology]

Steel heat treatment furnaces such as continuous steel annealing furnaces (approximately 600 to 1300
°C non-oxidizing atmosphere or Nz H2I N2 H
As shown in FIG. 4, the hearth roll that carries and transfers the steel material to be heated in a reducing atmosphere such as zCO, etc., has a roll shaft (10) and a roll body (20) fitted and fixed to the roll shaft (10).
), and has an internal water cooling structure that forcibly cools the roll body (20) and roll shaft (10) by supplying and discharging cooling water (W). Conventionally, the roll body (20) serving as the bearing surface for the heated steel material has been made of 5CH12,
High Cr-high Ni heat-resistant cast steels such as 5CI (22 (LrS G 5122)) have been used exclusively.

The problem with the amount of hearth rolls actually used in the heat treatment furnace is that build-up tends to occur on the surface of the body. Build-up is a phenomenon in which surface oxides (scale) and metal powder of steel adhere to the surface of the body (20) and adhere through chemical reactions, causing roughness and damage to the surface of the body. If this happens, the surface of the subsequent steel material will be flawed, causing a significant decrease in quality and yield.

As a countermeasure against this, recently the surface of the roll body has been made of Ni-based alloy (for example, 35Cr-10AI-0,5Y-Ni).
Attempts have also been made to coat the surface with ceramics such as alumina (Al□Os) or zirconia (ZrOz) by thermal spraying.

[Problems to be Solved by the Invention] Although it is possible to obtain a build-up reducing effect by coating the roll body surface with the Ni-based alloy, etc., it is not possible to maintain a stable build-up reducing effect under continuous furnace operating conditions. It is difficult to do so, and the effect is particularly small in a high temperature range exceeding 1000°C. On the other hand, ceramic sprayed coatings have low wettability to molten substances on the steel surface scale and exhibit excellent pill door knob resistance, but they have weak adhesion to the body surface and are themselves brittle materials, so they are mechanically and thermally resistant. It is prone to cracking and peeling due to impact, and has poor stability as a build-up prevention film.

The present invention has been made to solve the above problems.

[Means and effects for solving the problems] The hearth roll according to the present invention has a roll body having a surface layer formed by laminating multiple layers of cera (ivy film and metal film alternately and concentrically). It is characterized by

FIG. 1 shows a cross section of the body (20) of the hearth roll of the present invention. (21) is a trunk base material, and (22) is a surface layer that covers the surface of the base material. As shown in FIG. 2, the surface layer (22) has a ceramic film body (a+a+...) which is a build-up resistant material and a metal film (b, b,...
) has a laminated structure in which multiple layers are laminated through layers.

In the process of conveying steel materials by the hearth roll of the present invention,
If damage to the outermost surface (steel material bearing surface) of the surface layer (22) such as cracks, abrasion, or chips occurs due to the direct action of the steel material or the furnace atmosphere, the outermost surface will deteriorate as the damage progresses. The steel material is conveyed while repeating the process of replacing the film surface, which disappears from the roll surface (wears out or peels off), and the underlying film surface is exposed to the outermost surface and becomes a new steel material bearing surface.

Ceramic film (a+a+...) in the surface layer (22)
) are various oxides such as alumina, zirconia, titania, chromium oxide, silicon nitride, boron nitride, titanium nitride, chromium carbide, silicon carbide, tungsten carbide,
It may be a nitride-based ceramic, a carbide-based ceramic, or a mixture thereof (eg, alumina-zirconia, alumina-chromium oxide, etc.).

In particular, oxide ceramics such as Alkusu, etc.
It is suitable because it has excellent build-up resistance.

Surface N (22) with ceramic film (a+a+...)
The metal films (b, b,...) constituting the surface layer (2
2) has toughness, and ceramic films (a, a
+...) are separated and independent from each other, and even if a crack occurs in the outermost ceramic film due to mechanical or thermal shock, the propagation of the crack to the underlying ceramic film is blocked and damage is prevented. It also plays a role as a buffer and protective film.

The metal films (b, b, . . . ) are exposed at the outermost surface as the overlying ceramic film is damaged or peeled off, and becomes a steel support surface. The role of the metal film as a steel bearing surface may be temporary until the underlying ceramic film becomes a new steel bearing surface. Therefore, the metal membrane does not require durability or build-up resistance as a steel bearing surface.
It is formed using a metal material that is relatively easily abraded and peeled off and removed from the surface under the effects of load, impact, friction, etc. of the steel material that comes into contact with the membrane surface, as well as the direct thermal influence of the high-temperature atmosphere inside the furnace. be able to. Typical examples of metal films include iron or low iron alloys containing a small amount of alloy (eg, carbon steel, structural alloy steel, etc.).

The metal film formed from iron or low iron alloys oxidizes (scales) when it comes into contact with the atmosphere inside the furnace, and is removed from the body surface in a short period of time under the contact action of the steel material, so there is no possibility of steel scale etc. adhering to it. Even if the ceramic film is replaced by the underlying ceramic film without any progress of build-up, the surface of the body always maintains a healthy surface condition free of build-up.

However, it goes without saying that the metal film (b, b, ...) must not have the durability or build-up resistance as a steel bearing surface, but it must also have durability (e.g. wear resistance, heat resistance, etc.). ) or a metal having buildup resistance may be used to form the metal film.

Note that examples of metal film materials other than iron and iron low alloys include niobium (Nb), molybdenum (Mo), and tungsten (W).
) etc.

The thickness of the ceramic film (a) is not particularly limited, but if the film thickness is too thin, the film strength will be insufficient, and the film surface will be easily damaged due to mechanical/thermal shock, friction of steel materials, etc., and it will not be stable. The thickness is preferably about 5 μm or more, since this results in poor properties. However, if it is too thick, the durability will not be increased in proportion to the film thickness, and on the contrary, it will be more likely to cause cracks and peeling due to thermal stress, etc., so it is better to keep the film thickness up to 100 μm.
Usually, a thickness of up to about 50 μm is sufficient.

There are no particular restrictions on the thickness of the metal film (b), but
If it is too thin, the effect as a buffer/protection film for the underlying ceramic film (a) will be poor, so it is desirable that the thickness be about 10 μm or more, but there is no particular advantage in making it thicker than about 100 μm. If it is made too thick, it may cause congestion due to alternation of the membrane surface with the underlying ceramic membrane.
The advantages of having a composite laminated structure with a ceramic membrane will not be fully utilized. Therefore, it is preferable to limit the thickness to about 10 μm or more.

The above ceramic film (a+a+...) and metal film (b,
The layer thickness of the surface layer (22) consisting of b, . degree(
(usually about 1 to 3 seconds).

Ceramic film (a+a+...) and metal film cb,
The laminated film formation of b, . . . ) can be performed by the simplest and most economical thermal spraying method. Of course, other methods, such as powder sintering, are used to stack ceramic powder and metal powder having a predetermined composition as membrane materials around the body base material (21), and then apply pressure. It can also be formed by a firing treatment method. The body base material (21) may be made of, for example, carbon steel or various alloys (for example, 5CH13, 5CH2
2 etc.) may be selected and used as appropriate.

〔Example〕

(1) Production of test roll Hollow cylindrical body (outer diameter:
130 mm, body length: 480 mm) is used as the body base material (21), and a surface layer (22) is formed by alternately laminating a ceramic film and a metal film on the circumferential surface by a thermal spraying method. (22) was machined to a predetermined surface roughness, and the following two members A and B were obtained as test body parts (20). However, in both cases, the thickness of the Cera 1 film is approximately 40 μm.
The thickness of the metal film was approximately 60 μm, and the thickness of the surface layer (22) after machining was 3 m+n.

Ceramic film: Alumina metal film Niiron Sappu ± Ceramic film: Chromium carbide Metal film: Molybdenum Each of the above-mentioned body members A and B was fitted onto separately prepared roll shafts to form test rolls RA and R.

Assembled.

[■] In a build-up test test furnace (furnace temperature: 1150°C), the above-mentioned test rolls RA and RIl were arranged in parallel directions (interaxial path #: 200n+m) as shown in Fig. 3. A cylindrical ordinary steel material (outer diameter: 150+r+m
, length: 300mm), and each roll RA and R
6 was continuously rotated for 1000 hours at a rotational speed of 5 rpm, and the surface condition of the body of each roll and the conveyed material W was visually observed.

As a comparative example, 5C112, which is a typical conventional body material, was used.
Heat-resistant cast steel equivalent to 2 (25Cr-2ONi-1,5Si
-lMn-0,4C-F e)
The same build amplifier test as above was conducted on a hearth roll having the same body length as that of the above-mentioned test roll.

The body of the comparative roll after the above build-up test (SCH2
Significant build-up occurred on the surface of the sample rolls RA and Rm due to the adhesion reaction of scale, and numerous flaws were observed on the surface of the transported material.
In all of the (invention examples), there was no buildup on the body surface and the surface was smooth, and the conveyed material was found to have a healthy surface without any flaws. Note that the amount of diameter reduction in the body portions of the test rolls RA and RIl after the test was approximately 0.5 mm for the former and approximately 0.8 mm for the latter.

〔Effect of the invention〕

In the hearth roll of the present invention, the surface layer of the body that supports the steel material deteriorates during the repeated conveyance process of prepared material and is replaced with a new film surface of the lower layer one after another, resulting in build-up over a long period of time. The steel material is transported with the surface of the body always kept clean. Therefore, it is possible to use the roll body continuously for a long period of time without regenerating or reworking the surface, reducing the cost and labor required for roll maintenance, improving the operating efficiency of the heat treatment furnace, and improving the condition of the body surface. The effect of improving and stabilizing the surface quality of the heated copper material can be obtained by stabilizing the .

[Brief explanation of drawings]

Fig. 1 is a radial cross-sectional view showing the body of the hearth roll of the present invention, Fig. 2 is a radial cross-sectional view schematically showing the multilayer structure of the body surface layer of the roll of the present invention, and Fig. 3 is a build-up. 4 is an axial sectional view showing a conventional hearth roll. 10: roll shaft, 20: roll body, 21: body base material 2
2: body surface layer, a: ceramic film, b: metal film.

Claims (1)

[Scope of Claims] 1. A steel material with excellent build-up resistance, characterized in that the roll body has a surface layer formed by laminating ceramic films and metal films in multiple concentric layers alternately. Hearth roll for heat treatment furnace. 2. The hearth roll for a steel heat treatment furnace according to claim 1, wherein the metal film has a thickness of 10 to 100 μm, and the ceramic film has a thickness of 5 to 100 μm.